The present invention is generally directed to ink compositions and more specifically to ink jet ink compositions. More specifically, the present invention in embodiments is directed to ink compositions that are particularly suitable for use in known ink jet print processes, which inks contain a dendrimer, such as those as illustrated in copending patent applications U.S. Ser. No. 560,931, and U.S. Ser. No. 646,904, the disclosures of which are totally incorporated herein by reference. One embodiment of the present invention is directed to an ink composition which comprises an aqueous liquid vehicle, a dye, a glycol, and a dendrimer. The dendrimer can be admixed with the ink components to form the final ink jet composition which in embodiments possesses excellent waterfastness characteristics, such as about 80 to about 95 percent. Examples of ink jet printing processes, including thermal ink jet, are illustrated in U.S. Pat. Nos. 4,601,777; 4,251,824; 4,410,899; 4,412,224 and 4,532,530, the disclosures of which are totally incorporated herein by reference.
Ink jet printing systems generally are of two types, continuous stream and drop-on-demand. In continuous stream ink jet systems, ink is emitted in a continuous stream under pressure through at least one orifice or nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the orifice. At the break-up point, the droplets are charged in accordance with digital data signals and passed through an electrostatic field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or to a specific location on a recording medium. In drop-on-demand systems, a droplet is expelled from an orifice directly to a position on a recording medium in accordance with digital data signals. A droplet is not formed or expelled unless it is to be placed on the recording medium.
Since drop-on-demand systems require no ink recovery, charging, or deflection, the system is much simpler than the continuous stream type. There are two types of drop-on-demand ink jet systems. One type of drop-on-demand system has as its major components an ink filled channel or passageway having a nozzle on one end and piezoelectric transducer near the other end to produce pressure pulses. The relatively large size of the transducer prevents close spacing of the nozzles necessary for high resolution printing, and physical limitations of the transducer result in low ink drop velocity. Low drop velocity seriously diminishes tolerances for drop velocity variation and directionality, thus impacting the system's ability to produce high quality copies, and also decreases printing speed. Drop-on-demand systems which use piezoelectric devices to expel the droplets also suffer the disadvantage of a slow printing speed.
One type of drop-on-demand system is known as thermal ink jet or bubble jet, and this sytem apparently enables high velocity droplets and allows for the very close spacing of nozzles. The major components of this type of drop-on-demand system are an ink filled channel having a nozzle on one end and a heat generating resistor near the nozzle. Printing signals representing digital information originate an electric current pulse in a resistive layer within each ink passageway near the orifice or nozzle, causing the ink in the immediate vicinity to evaporate almost instantaneously and create a bubble. The ink at the orifice is forced out as a propelled droplet as the bubble expands. When the hydrodynamic motion of the ink stops, the process can be repeated. With the introduction of a droplet ejection system based upon thermally generated bubbles, commonly referred to as the "bubble jet" system, the drop-on-demand ink jet printers provide simpler, lower cost devices than their continuous stream counterparts, and yet have substantially the same high speed printing capability.
The operating sequence of the bubble jet system can be initiated with a current pulse through the resistive layer in the ink filled channel, the resistive layer being in close proximity to the orifice or nozzle for that channel. Heat is transferred from the resistor to the ink. The ink becomes superheated far above its normal boiling point, and for water based ink, finally reaches the critical temperature for bubble formation or nucleation of around 280.degree. C. Once nucleated, the bubble or water vapor thermally isolates the ink from the heater and no further heat can be applied to the ink. This bubble expands until all the heat stored in the ink in excess of the normal boiling point diffuses away or is used to convert liquid to vapor, which removes heat due to heat of vaporization. The expansion of the bubble forces a droplet of ink out of the nozzle, and once the excess heat is removed, the bubble collapses on the resistor. At this point, the resistor is no longer being heated because the current pulse has passed and, concurrently with the bubble collapse, the droplet is propelled at a high rate of speed in a direction towards a recording medium. The resistive layer encounters a severe cavitational force by the collapse of the bubble, which tends to erode it. Subsequently, the ink channel refills by capillary action. This entire bubble formation and collapse sequence occurs in about 10 microseconds. The channel can be refired after 100 to 500 microseconds minimum dwell time to enable the channel to be refilled and to enable the dynamic refilling factors to become somewhat dampened. Thermal ink jet processes are well known and are described in, for example, U.S. Pat. No. 4,601,777, U.S. Pat. No. 4,251,824, U.S. Pat. No. 4,410,899, U.S. Pat. No. 4,412,224, and U.S. Pat. No. 4,532,530, the disclosures of each of which are totally incorporated herein by reference.
In copending patent application U.S. Ser. No. 646,904, the disclosure of which is totally incorporated herein by reference, there is illustrated an ink composition which comprises an aqueous liquid vehicle and colored particles comprised of a dendrimer core colored with a dye or dyes covalently attached thereto. The aforementioned ink usually contains water, and as optional additive components known humectants, and known biocides.
In a patentability search report for copending application U.S. Ser. No. 646,904, the following United States Patents were recited: U.S. Pat. No. 4,705,567 relating, for example, to heterophase ink compositions comprised of water and a dye covalently attached to a polyethylene glycol, or polyethylene imine component, which component is complexed with a heteropolyanion; U.S. Pat. No. 4,623,689 which discloses, for example, an ink for ink jet recording wherein the ink contains a certain aqueous colored polymer, see the Abstract for example; and as collateral interest U.S. Pat. Nos. 4,664,708; 4,680,332 and 4,791,165. The disclosures of the aforementioned patents, and all other patents mentioned herein are totally incorporated herein by reference.
Copending application U.S. Ser. No. 544,564, the disclosure of which is totally incorporated herein by reference, relates, for example, to ink compositions which comprise an aqueous liquid vehicle and colored particles of an average diameter of 100 nanometers or less which comprise micelles of block copolymers of the formula ABA, wherein A represents a hydrophilic segment and B represents a hydrophobic segment, and wherein dye molecules are covalently attached to the micelles. In a specific embodiment of the copending application, the colored particles comprise micelles of block copolymers of the formula ABA having silica precipitated therein and dye molecules covalently attached to the micelles. Another embodiment of the copending application is directed to a printing process which comprises incorporating the ink thereof into an ink jet printing apparatus and causing droplets of the ink to be ejected in an imagewise pattern onto a substrate, thereby generating images on the substrate. Also, in another embodiment of the copending application there is disclosed an ink preparation process which comprises, in the order stated, (1) adding to water a block copolymer of the formula ABA, wherein A represents a hydrophilic segment and B represents a hydrophobic segment, thereby forming a dispersion of micelles of the block copolymer; (2) adding a water-soluble base to the dispersion, thereby bringing the pH of the dispersion to at least 8; (3) adding to the dispersion a solution comprising water and a reactive dye capable of reacting with the block copolymer, thereby forming colored polymeric micelles; and (4) admixing the colored micelles with an aqueous liquid vehicle to form an ink composition.
Heterophase inks containing pigment particles as colorants, however, also exhibit difficulties. For example, the particulate colorant may exhibit a tendency to settle out or separate from the liquid vehicle, particularly when the ink is stored for long periods of time. In addition, inks containing pigment particles as colorants tend to be opaque instead of transparent, which reduces their usefulness for printing images on transparencies for the purpose of overhead projection. Further, inks containing pigment particles as colorants tend to clog the narrow orifices of the printhead resulting in deterioration of the print quality. These and other disadvantages, such as poor resistance to rubbing, by another substrate or by hand are avoided, or minimized with the inks of the present invention.
Although known ink jet compositions are suitable for their intended purposes, there remains a need for ink compositions suitable for use in ink jet printing processes. In addition, a need remains for ink compositions particularly suitable for thermal ink jet printing processes. Further, there is a need for ink compositions that exhibit rapid drying times. There is also a need for ink compositions which when applied on paper in an ink jet printing process generate prints with excellent waterfastness characteristics. More specifically, there is a need for ink compositions with aqueous liquid vehicles and dendrimers that exhibit improved waterfastness compared to aqueous inks without dendrimers. A need also remains for ink compositions exhibiting acceptable lightfastness characteristics when printed on a suitable substrate, such that, for example, there is no more than a 20 percent decrease in optical density of the printed areas after several weeks of exposure to ordinary light in the normal environment intended for the use of the printed material. Further, there is a need for ink compositions that are nontoxic and nonmutagenic. In addition, a need exists for ink compositions for which a wide variety of color choices exists. There is also a need for ink compositions that can be prepared by simple and economical processes. Further, there is a need for ink compositions suitable for printing on plain papers, coated or treated papers, and transparency materials. In addition, there is a need for ink compositions that when printed on substrates exhibit excellent optical density, low feathering, for example there is minimal undesirable bleeding of the ink in areas adjacent to the printed images, and excellent rub resistance, for example after strong hand rubbing for an extended period of time, about up to three minutes in embodiments, the image is not removed or disturbed. There is also a need for ink compositions that when used to print on transparency materials generate images that project their original colors when light is passed through the image. A need also remains for ink compositions with acceptable thermal stability, for example the inks are not substantially adversely effected in the printhead by heat, and storage stability. Further, there is a need for ink compositions suitable for ink jet printing that do not induce clogging of the printhead. A need also remains for ink compositions that when printed on substrates exhibit no undesirable intercolor bleeding between areas of different color.